(I made a mistake and posted this in the general discussion forum first, but realized later I'm asking a technical question so here it is here, sorry)

My 85 C4 is showing a couple of transmission quirks. First, I'm a relatively new corvette owner, but quite mechanical. I've been told that this car with 190,000 km had a transmission overhaul within the last 50,000. It shifts fine, all gears are smooth etc. Once when accelerating up a bit aggressively, it blew some fluid out and hit the exhaust, lots of smoke but everything still works fine. There doesn't seem to be any leaking at the front or rear seal after I wiped it down. Some have said that it if the 700 tranny (on all GM's) is overfilled this can happen as there is an overflow near the top of the tranny. I've also been told that the 700 tranny doesn't have a large enough return hole near the front seal and this can be fixed by drilling it a bit larger. Any thought or comments or experiences?

The second problem is I get a good vibration when it is unlocking the torque converter esp when there is a little torque being applied. Some have suggested it might be as simple as the torque converter switch and best to change that before pulling the tranny out. Comments??

Thanks!

 

Everything you said makes sense.Early pumps hade problems. They are easily fixed by drilling some holes larger and replacing the front pump bushing and seal as well. Install a seal retainer if the car does not have one already. The converter vibration is a common sign of pending failure. It can be tested for excessive endplay while it is out.

 

Thanks for your suggestions, Pete - do you think it is worth replacing the torque converter lock up switch before I drop the tranny to get rid of the vibration or do you figure the torque converter is on its way out? I might have to anyway esp. if I'm going to be drilling the holes and replacing the seal. Also wonder if the tranny is a recent rebuild (I haven't been able to confirm this yet) it might have had a torque converter replaced then and maybe a good full flush would make a difference. Trying not to get my hands to dirty!! ha!

 

I hate to be the voice of doom, but it sounds like the torque converter is on its way out. I could be wrong though. You can drop the pan and ohm test the solenoid. It should read approx 20 ohms at approx 70 degrees f. You can also pull out the pressure switches and air check them. If they leak change them. If the test bad using a continuity tester, change them. Some are normally open and some are normally closed. During a typical rebuild one or both pressure switches are usually bad. So you could get lucky. You do not have to disassemble valve body. All of these parts are easy to check with the pan down. If all is good after this, assume a bad converter. You cannot make the pump mods without pulling the pump, dissassembling it completely, and rebuilding it. If you go this far, pick up a used 10 vane pump, plug the aux v/b feed hole and use it. MUCH better pump and it is already improved(no drilling). If you need more help, just ask. Pete

 

Thanks for the info Pete - sounds like you've been into a few 700's in your time! As you can probably guess, with me being in Northern Ontario, my C4 is sleeping soundly and will be for the next 2 or 3 months. Unfortunately, it is all wrapped up under a winter shelter in my back yard surrounded by a couple of feet of snow. (had to make room for the wife's car and the sleds in the garage!) So, when the spring weather comes around, I'll be dropping the pan first to see what I find. I wish I knew the history for certain and if there was a tranny rebuild, exactly what was done. I might be a little more certain when I take the pan off.
You'll probably be hearing from me again on this one!